The present invention relates to a system for controlling the fuel delivery of an electronic injection system.
Known electronic injection systems present an electronic control system with a processing unit for receiving and processing signals proportional to engine speed and air pressure and temperature in the intake manifold, and accordingly supplying an output value (Q.sub.b) indicating the amount of fuel to be injected for achieving a substantially correct stoichiometric air/fuel ratio.
The output value (Q.sub.b), which is normally determined by means of memorized tables, is modified by monitoring the composition of the exhaust gas with the aid of a sensor inside the exhaust manifold, which supplies a signal ranging from 0 to 1 V, depending on whether the air/fuel mixture contains more or less fuel as compared with the required stoichiometric ratio.
The signal from the sensor is processed with the aid of a proportional-integral controller for obtaining a correction factor (K.sub.02) by which the previously calculated fuel quantity value (Q.sub.b) is modified to give the correct fuel quantity (Q.sub.bc). This therefore provides for closed-loop control of the amount of fuel injected, by virtue of feeding back the signal supplied by the sensor.
The exhaust sensor presents a transfer function simulatable by a nonlinear characteristic and a time delay, which is substantially the time interval between the instant in which the air/fuel mixture departs from the stoichiometric value and the instant in which the sensor switches subsequent to detecting the variation.
To this is added a further delay, between the instant in which the fuel is injected and the instant in which departure from the stoichiometric ratio is detected, due to the time taken to travel along the intake manifold, undergo combustion, and travel along the exhaust manifold.
The above delays seriously impair the response and dynamic performance of the system as a whole, by virtue of the exhaust sensor signal failing to correspond with the actual composition of the air/fuel mixture.
Particularly under transient operating conditions of the engine (corresponding, for example, to sharp variations in supply pressure), the correction factor (K.sub.02) fails to provide for adequately correcting the fuel quantity determined by the processing unit, thus resulting in the air/fuel ratio departing substantially from the stoichiometric ratio.